1. Field of the Invention
The present invention relates to a water quality monitoring apparatus using aquatic living things for observation of the quality of raw water, where raw water is introduced into a water tank for breeding or raising aquatic living things, and the water tank is taken through a video camera or the like to perform an image or picture analysis of action patterns of the aquatic living things.
2. Description of the Related Art
So far, in a filtration plant or the like there has been provided an apparatus in which aquatic living things such as fish being under observation are raised within a water tank, which continuously receives raw water, to be taken through an industrial television camera or the like so that the taken image is analyzed to grasp the fish's action pattern on the basis of the position at which the fish under observation swims and an alarm is raised if the fish takes an abnormal action. For example, for detection of the position of the fish under observation, the images photographed at a given time interval are stored in an image memory and an image portion corresponding to the fish under observation is recognized by the formation of a differential image between two adjacent images and the position and travelling speed of the fish under observation are detected on the basis of the variation of the position of the center of gravity of the same image portion so that the detected position and travelling speed are compared with the velocity distribution prestored in the normal conditions to detect the abnormality of the water quality (Japanese Patent Publication No. 6-68489).
There is a problem which arises with the above-mentioned prior apparatus, however, in that, since the comparison is made for all the fixed pixels in the image memory, its information quantity is too much to cause the necessity of a long processing time, and when an image other than the water tank comes to within the photographing range of the television camera, the comparison is reluctantly made even for the portions which do not require the comparison, which can make the accurate detection difficult. For these reasons, it is necessary that the water tank is photographed in a state that the entire water tank coincides with the photographing range of the industrial television camera so that all the pixels in the image memory always correspond to the image of the water tank. However, in this case, difficulty is encountered to facilitate the location of the television camera.
In addition, since the above-described prior apparatus is made to compare the travelling speed of the fish under observation with the velocity distribution obtained at the time of the normal conditions, although the detection is possible when the fish takes the typical abnormal action, if the fish takes an action close to an abnormal action, for example if the fish rises to have bait, a judgment to the abnormality can be made in error, and hence it is difficult to accurately decide, through only the comparison with the velocity distribution in the normal conditions, the abnormal action taken for when the water quality is abnormal.